Dental stress breaker former



Nov. 30, 1954v H. w. AMES 2,695,433

DENTAL STRESS BREAKER FORMER Filed Oct. 8, 1953 rill/43" INVENTOR. How/W0 M AMES TTOANEY- United States PatentO DENTAL STRESS BREAKER FORMER Howard Wesley Ames, Santa Monica, Calif.

Application October 8, 1953, Serial No. 384,849

1 Claim. (Cl. 22-160) This application is a continuation-in-part of my application Serial No. 121,784, filed October 17, 1949, now abandoned, for Dental Stress Breaker Former and Method of Making Dentures.

This invention relates to the making of dentures of the type ordinarily referred to as partial plates and bridges and has as its general object to provide improved means for and method of making a denture having a stress breaker or pivotal connection between the frame of the denture and any of the clasps by which it is attached to a patients teeth. Such stress breakers are used for the purpose of relieving the prying action that may be exerted through the clasp against the tooth embraced thereby, when pressure is applied to an area of the frame at a distance from the clasp and is transmitted to the clasp through a rigid connection between the frame and the clasp. The pivotal connection permits some movement of the frame relative to the clasp during mastication, allowing the clasp to remain in a fixed position, unalfected by such movement. Stress breakers in the form of pivotal joints having shanks adapted to be soldered respectively to the clasp and to the frame, are commonly used by dentists and dental laboratories but are fairly expensive and the operation of soldering them in place is a somewhat difficult and delicate one and time consuming and therefore expensive. One of the objects of the present invention is to provide for forming a stress breaker joint in a denture without the requirement of soldering any part thereof to the frame or clasp. To this end, the invention contemplates a joint forming unit and a method of utilizing the same in fabricating a denture, whereby a stress breaker joint integrally cast in the frame and on the clasp respectively, is formed.

One aspect of the invention is the provision of a prefabricated unit having generally the form and dimensions of the stress breaker joint that is to be formed in the denture, which unit is incorporated into the casting pattern of wax or other material that is used to shape the mold cavity and then melted or burned away from the mold cavity prior to the casting process by baking the mold in a furnace. The joint forming unit includes parts that are burned away in this baking step, and are replaced by the gold of the casting. It also includes a separator part that is resistant to the heat of the casting process. This separator part forms the separation between the respective sections of the stress breaker joint in the finished casting. The separator part is of a material which, subsequent to the casting operation, may be removed by a process step (such as by dissolving it in acid) which does not affect the cast gold parts. Thus there remains, between the frame and the clasp, an integrally cast pivotal stress breaker joint.

An object of the invention is to provide a novel joint forming unit which may be utilized in the manner outlined above.

Another object is to provide a novel and improved method of forming an integrally cast stress breaker joint between a denture frame and a tooth engaging clasp.

Other objects will become apparent in the ensuing specifications and appended drawings, in which:

Fig. l is a plan view of a partial plate denture embodying the invention, parts thereof being broken away and shown in section to better illustrate my improved stress breaker joint;

Fig. 2 is a plan view of the joint forming unit, partially in section;

2 Fig. 3 is a cross-sectional view of the same; Fig. 4 is a side view of the same; a Fig. 5 is a partial plan view of a casting model incorporating the joint forming unit in one of the steps of my improved process;

. Fig. 6 is a partial plan view of a casting made from the casting model shown in Fig. 5, illustrating a subsequent step in my process; a

Fig. 7 is a partial plan view of the casting shown in Fig. 6 at a subsequent stage of processing;

Fig. 8 is an enlarged sectional view of the improved stress breaker joint of my invention; and

Fig. 9 is a side view of the joint.

Referring now to the drawings in detail, I have shown in Fig. 1 a partial plate denture embodying generally a frame 10, adapted to extend from one side of the jaw to the other, a single tooth 11 mounted at one end of the frame and a pair of teeth 12 and 13 mounted at the other end of the frame. The frame 10 includes a bridge portion 14 and a pair of opposed tooth engaging clasps 15 and 16 at one end thereof. At the other end of the bridge 14, the frame includes an open loop section 17 which provides a reinforcing support for a flesh tinted panel 18 of plastic material, underlying the teeth 12 and 13. As shown, the frame includes an extension 19 which provides a fulcrum to bear against the roof of the mouth toward the front of the jaw, in accordance with common practice. A third clasp 20 is embraced between the loop sections 17 of the frame and the extension 19.

The clasps 15 and 16, balanced on both sides of tooth 11, distribute the pressure against tooth 11 substantially equally to both of the adjacent teeth, and with little prying action resulting from such pressure. On the other side of the denture however two teeth 12 and 13, lined up with claps 20 on the same side thereof, would, under masticating pressure, be capable of exerting considerable prying action against the tooth embraced by clasp 20 if rigidly connected thereto. Accordingly, a stress breaker joint between clasp 20 and teeth 12 and 13 is needed and is provided for in the denture shown.

Fig. 8 illustrates an enlarged sectional view of this stress breaker joint. Clasp 20 has a shoulder 21, from which a straight, parallel sided arm 22 projects. Intermediate its ends, arm 22 includes a pair of semi-spherical sockets 23, directly opposed on a common hinge axis which extends transversely through the center of arm 22, at right angles to the side faces thereof. Clasp 20, arm 22, and sockets 23 are in the form of an integral casting.

Arm 22 is received between jaws 24 and 25 respectively, cast integrally in frame 10. As shown, jaw 24 constitutes the end portion of the outer lobe of frame loop 17, and jaw 25 is formed on extension 19. laws 24 and 25 have flat opposed faces lying closely adjacent and parallel to the flat side faces of arm 22, and are provided with seim-spherical trunnions 26 received in sockets 23. The spacing between the opposed faces of jaws 24 and 25 and arm 22 and of trunnions 26 and sockets 23 may be in the neighborhood of one-thousandth of an inch. Thus there is a fairly snug engagement between arm 22 and jaws 24,

25 and between trunnions 26 and sockets 23, providing a hingle about which clasp 20 may swivel on the aforesaid hinge axis.

The joint just described is shaped and formed by the use of the joint former shown in Figs. 2, 3 and 4. This oint former comprises a yoke shaped shim 27 of thin sheet metal subject to being dissolved by a suitable acid. For example, sheet metal, which will dissolve quite readily in nitric acid, may be used, and is preferred. The shim 27 includes a pair of side arms 28, extending in spaced parallel relation and a pair of end flanges 29 extending outwardly in opposite directions from the free ends of arms 28. The thickness of shim 27 corresponds to the width of the spacing between jaws 24, 25 and arm 22, and the spacing of the inner sides of arms 28 corresponds to the thickness of arm 22. Intermediate their ends, arms 28 are provided with dimples 30 projecting inwardly toward each other. The dimples 30 correspond to the spaces between trunnions 23 and sockets 26. The outer faces of shnn 27 are covered by a yoke shaped sheath 31 of plastic material, preferably a rigid organic material snugly embracing the shim. The inner faces of shim 27 are COVETGG by a Cffi 32, 211$?) 6f fillCll lilfistiti ifiitflal, which is embraced between arms 28. Core 32 has an end portion 33 which projects beyondfianges 29 and partially covers the forward faces thereof; Sheath 31 and core 32 may be secured in assembled relation with shim 27 by means of a stem 34 formed integrally on the end of core 32, projecting through registering openings in shiin 27 and sheath 31, and attached to the latter in any suitable manner conventional in plastics processes, such as by having its end spread by the application of heat and pressure thereto, or by establishing a bond between the end of the stem and sheath 31,- throu h the use of a solvent for the plastic.

in utilizing the former in the fabrication of a denture, the technician follows the conventional steps of casting a master model against a negative impression of the patients mouth, preparing a casting model in heat 'resistant investmentr'naterial, to form one section of the casting mold, and then waxing up a casting pattern on this casting model.- Such pattern corresponds to the gold frame structure of Fig.- l in all parts thereof except the stress" breaker joint; That portion of the pattern which corresponds to theportion of the frame embodying the stress breaker,- is shown in Fig. 5, and is indicated gem orally at 19a. It includes the counterparts of each part of the frame 10,- the extension portion being indicated at 1941, the open loop portion at 17a, and the clasp portion (correspondin to clasp 20) being indicated at 20a.

In the waxing step, an appropriate gap is left in the wax' pattern, between clasp portion 20a and loop portion 17a and in loop portion 17a, to receive the joint former, which is inserted into this gap and its end portion33 ressed into the shoulder 21a of claw portion 20a after such shoulder has been suitably heat softened. The sides of the joint former are attached to the Walls of the gap in 100p member 17a, as by drops of melted wax applied in proper positions to bridge" between the respective sides of the jointformer and the adjacent areas of loop men) ber 17a;

The casting model, with the pattern thereon,- is then invested in a body ofinv'esting material, to form the other half of the mold, and a suitable openingis formed, in ac"- cordance with conventional practice. The mold is then baked in a furnace to burn out the pattern. In this step, the plastic parts 31 and 32 of the joint former are burned away, leaving mold cavities which are joined to the mold cavities from which the pattern wax has beenmelted.

The edge portions of shim 27, which, in the joint former, projected beyond the plastic parts 31 and 32 as indicated in Figs. 3 and 4, will be embedded in the mold, thus securely holding shim 27 in a position in which it provides the desired separation between sections of the mold cavity in which the stress breaker joint is to' be formed.

The mold isflthen placed in a centrifuge, molten gold is introduced therein, and the centrifuge is operated to force the gold into the mold cavities, in accordance withconventional practice. Subsequently, the gold castingl thus formed is: removed from the mold, the joint portion hay ingtthe'form shown in Fig. 6; in which the joint is bridged by a member 35 which integrally joins the separated parts of' loop 17 around the separating shim 27. With the parts thus: rigidly heldtogether by this bridging connec tion, the casting is subjected to the conventional cleaning, grinding and polishing operationsto' bring it to the desired state of final shape and finish.

The bridging. member 35 is then cutaway in any suitable manner, as; by the use of a dentistsburr.- This step is illustrated in Fig; 7, in which the dotted lines indicate theformer position of the bridging member. In this cutting. step, the central web' portion of shim 27 is-also cut it way; leaving it in two separate halves,v as shown in As a final step in the process of fabricating the joint, the casting is immersed in nitric acid or other suitable solvent for the metal of shim 27, and the remaining halves of the shim are eaten away entirely, leaving'the jointas shown in Fig. 8';

The shoulder member 21 of clasp 20, as shown in Fig. 9, is-spaced slightly frdiii the efid 6f the nos 24, 25, 53 spaces formed by the dissolving away of flanges 29. Shoulder member 21 will, in the finished denture, coact with the ends of jaws 24, 25 to limit the hinging movement of the joint. If additional movement is desired, these spaces may be widenedby inserting a burr therein and cutting away either the shoulder 21 or jaws 24, 25, preferably theformer;

The dissolutio" of the separator shi'rn may be eliected either by the use of astrong acid, such as nitric acid, which will dissolve steel unassisted by any other agency, or by the use of a suitable solution, aided by an electric current to dissolve by electrolytic action, a solution which will not produce any electrolysis of the gold parts, being selected. The term chemical dissolution, as used herein, is intended to include such an electrolytic type of distiotit I claim: i I V K A joint rennet for as a part of a casting pattern ployed in fabricating a denture includinga' frame and a solution as well as the more simple type of dissolving acensp connected arenas tsy a stress b eaker e at ir'lt e rorrn of a hinge including an arm having opposed parallelfiat sides,- a pair of jaws having opposed parallel flat faces embracing said flat sides,- and opposed, axially aligned hinge trunnions and mating tannin" sockets formed iii teg rally in said arm and jaws and ging with said sides and faces, said joint former edriiprising}: a iiiiitafy assertibly of pattern parts in sandwich form, said pattern pans comprising a central part for shaping said arm, spaced outer parts for shaping said jaws and a pair or separator parts sandwiched between said central and outer pafts with the outer parts in embracing relation to the central part and with the separator parts interposed between said central part and said outer p'art's, said sep'a'i-atbf parts he izrg of sheet material of extreme thinness in relation to the thickness of said central and outer parts,= said central and outerparts being of arigid organic material subject to be ing burn-ed away by baking the same in a furnace and said separator parts being of a material subject to being" dis solvedand washed away by a corrosive liquid, said separator parts being in spaced, parallel relation,- and the outer faces of said central part and the inner'fa'ces' of said outer parts being in face to face contact with the respe'c' tiye surfaces of saidseparator parts so asto establish par-"- allel planes of relative oscillatory bearing engagernent be: tween adjoining faces of said arm and jaws in the finished stress breaker joint, said separator parts having many aligned dimples projecting laterally from said planes and beyond the planes of adjacentfaces'of the other parts; the inner and outer surfaces of said dimples defining respecti-vely saidtrunnions' and trunnion sockets in the finished joint, with said trunnions ,fit'ted closely into said sockets to establish hinged connections between said arm and jaws."

lieferences Cited in the tile of this patent- I UNITE STATES Pariah-Ts Number Name Date 366,113 Keep et al I11ly 5, 1887 1,087,435: Canda Feb: 17, 1914. 1,221,459 rug Apr; 3 1917 2,129,861 Morton Sept. 13, 1938'. 2,205,096 Eccles June l8; 1940' 2,227,735 Morton Jan. 7, 194-1 2,362,875; ahnL .2 Nov. 14, 1944 2 ,476,294, Milton, Jr., et al. '-,I;uly 26, 1949: 2,487,965 Dresser Nov. 15:,- 1-949. 2,5 02,337 Moir Mar; 28, 195.0. 2,508,546 Skinner May 2-3,- l950 FOREIGN PATENT Number Country, M Date 549,016 Great" Britain Nov. 3, 1942 

